In continuous casting of metals, scrap is melted in a furnace such as an electric arc furnace. The molten metal is typically tapped from the furnace to a ladle. The ladle is a vessel that may be a moveable, and which transports the molten metal to another vessel, a tundish, which acts as an intermediate storage vessel. From the tundish, the molten metal can be tapped into a mould.
FIG. 1 depicts a schematic cross-sectional side view of a vessel containing molten metal 3a. A primary flow 1a, generally having a flow direction in the casting direction, is created in the molten metal 3a contained in the vessel 5. Moreover, a secondary flow 1b, inter alia flowing towards the meniscus 3b, i.e. the surface of the molten metal 3a, is also created.
The primary flow and the secondary flow can be created in a vessel such as a mould for example due to vertical oscillation O of the vessel. The oscillations prevent solidified cast material to adhere to the inner mould walls. The movement in the molten metal causes bubbles and impurities in the melt to be transported in the casting direction. Therefore the molten metal is preferably controlled during the casting process, for instance by means of magnetic fields, such that the above-mentioned problems are reduced.
EP 1172158 discloses a method and an apparatus for continuous casting of metals. In this document, several coils are arranged at a casting mould such that the molten metal flow can be controlled properly. A plurality of coils are used for providing a static as well as a moving magnetic field in the melt.
EP1623777 discloses a continuous casting method for steel. At least three electromagnets are disposed along the longitudinal direction of a mould. While the electromagnets generate a vibrating magnetic field, peak positions of the vibrating magnetic field is shifted in the longitudinal direction of the mould.
JP10305353 discloses a process for continuous moulding of steel comprising arranging magnetic poles as upper and lower two stairs at the back face of a long side of a mould to place the long side of the mould between the upper and lower sides of a discharge hole of a dipping nozzle and controlling a flow of the molten steel in the mould by charging magnetic fields. The magnetic fields charged by the magnetic poles are made so as to be at least the magnetic field charged by the lower magnetic pole is a magnetic field superimposed by a direct current static magnetic field (DC-StMF); and an alternating current shifting magnetic field (AC-ShMF) or the magnetic fields charged by the upper magnetic pole is a magnetic field superimposed by the DC-StMF and the DC-ShMF and the magnetic field charged by the lower magnetic pole 8 is the DC-StMF.
JP5154623 discloses a method for controlling fluidity of molten steel in a mould. Three phase coils for electromagnetic stirring are arranged to the continuous casting mould and DC current periodically varying current value in conducted in each phase and the phase of variation of current value in each phase is shifted by 120 degree angle.
EP1510272 discloses a method for producing ultra low carbon steel slabs. An ultra-low carbon steel slab having a carbon content of about 0.01 mass percent or less is produced by casting at a casting speed of more than about 2.0 m/min using a mold provided with a casting space having a short side length D of about 150 to about 240 mm and an immersion nozzle provided with discharge spouts each having a lateral width d, the ratio D/d being in the range of from about 1.5 to about 3.0.
WO2008004969 discloses a method for controlling a flow of molten steel in a mould by applying at least one magnetic field to the molten steel in a continuous slab casting machine. This is achieved by comprising controlling a molten steel flow velocity on a molten steel bath surface, meniscus, to a predetermined molten steel flow velocity by applying a static magnetic field to impart a stabilizing and braking force to a discharge flow from an immersion nozzle when the molten steel flow velocity on the meniscus is higher than a mould powder entrainment critical flow velocity and by controlling the molten steel flow velocity on the meniscus to a range of from an inclusion adherence critical flow velocity or more to a mould powder entrainment critical flow velocity or less by applying a shifting magnetic field to increase the molten steel flow when the molten steel flow velocity on the meniscus is lower than the inclusion-adherence critical flow velocity.
Gardin P et al: “CC électromagnétique de brames: Développement de modéles numériques de la configuration AC+DC en longotiére/Electromagnetic casting of slabs: Development of numberical models for an AC & DC configuration in the mould” discloses a new concept of electromagnetic continuous casting of slabs, in which an alternating magnetic field (AC) with middle range frequency is combined with a continuous magnetic field (DC) in the vicinity of the mould meniscus.